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答:这与血清中胆红素的含量有关。胆红素主要来源于衰老红细胞崩解后的血红蛋白,也有一小部分来源于血红蛋白以外的其他卟啉化合物,如肌红蛋白、过氧化酶、过氧化氢酶及细胞色素等。体内红细胞不断地更新着,衰老红细胞主要在肝、 相似文献
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【目的】从菌株Streptomyces albus DSM 41398的发酵产物中发掘结构多样的由I型聚酮合酶催化形成的化合物,以期找到具有新颖结构或强生物活性的化合物。在结构鉴定的基础上,对其生物合成途径进行分析。【方法】利用HPLC分析方法,通过系统比较野生型菌株S.albus DSM 41398与I型聚酮合酶编码基因簇失活突变株的发酵产物差异,实现目标化合物的定向分离。然后,利用~1H-和~(13)C-NMR以及HR-ESI-MS进行化合物的结构鉴定。最后,利用生物信息学等方法对化合物的生物合成途径进行推测和分析。【结果】从5 L的S.albus DSM 41398发酵产物中,分离得到了2个具有抗肿瘤活性的聚酮类化合物放线吡喃酮和洋橄榄菌素,分别定位了它们的生物合成基因簇,并分别对其生物合成途径进行了推导。其中,放线吡喃酮的生物合成基因簇为首次报道。【结论】本研究一方面为基因组发掘S.albus DSM 41398中其他由I型聚酮合酶催化形成的化合物提供参考,另一方面也为相关化合物的结构修饰改造奠定了良好的基础。 相似文献
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《生物加工过程》2020,(3)
多酚氧化酶在昆虫的变态发育和免疫防御中起着非常重要的作用,可作为害虫控制的一个重要作用靶标。采用40%饱和度硫酸铵沉淀和Sephadex G-100凝胶过滤等步骤,对产自于乌鲁木齐的春尺蠖幼虫多酚氧化酶进行分离,并研究其酶学性质。结果表明:多酚氧化酶的比酶活为617.21 U/mg,是粗酶液的6.06倍;该酶对焦性没食子酸、邻苯二酚和L-多巴的K_m值分别为6.45、1.11和1.3 mmol/L;在pH 6.5、25℃时,多酚氧化酶活性最高;当温度高于45℃时,随着保温时间的延长,酶活力下降明显。采用中压色谱和C18反相制备型色谱技术对尖果沙枣叶乙醇提取物进行分离,得到6个化合物,鉴定了其中2个化合物;将这2个化合物用于多酚氧化酶的抑制实验,结果表明分离到的化合物6和化合物7均显示出抑制活性,IC_(50)值约为0.125 mg/mL。 相似文献
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植物三萜化合物是一类具有6个C5异戊二烯单元的高附加值天然化合物,具有抗炎、护肝、抗肿瘤、抗氧化和降血压等重要药理活性。在三萜化合物生物合成过程中,细胞色素P450酶通过引入羟基、羧基、羰基以及环氧基等官能团,为丰富三萜结构的多样性起到了重要的作用。然而,目前P450酶底物催化特异性机制仍不清晰,异源底盘细胞中表达率低、与细胞色素氧化还原酶(CPR)的适配性差限制了其在植物三萜化合物微生物异源合成中的应用。本文系统地介绍了植物三萜化合物的合成途径、P450酶的催化系统组成和催化机制。通过P450酶的理性与非理性的分子改造,P450酶及其CPR的适应性匹配以及关键代谢途径的区室化研究,以期为P450酶在高效合成三萜化合物的应用提供研究思路。 相似文献
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Epoxides are attractive intermediates for producing chiral compounds. Important biocatalytic reactions involving epoxides include epoxide hydrolase mediated kinetic resolution, leading to the formation of diols and enantiopure remaining substrates, and enantioconvergent enzymatic hydrolysis, which gives high yields of a single enantiomer from racemic mixtures. Epoxides can also be converted by non-hydrolytic enantioselective ring opening, using alternative anionic nucleophiles; these reactions can be catalysed by haloalcohol dehalogenases. The differences in scope of these enzymatic conversions is related to their different catalytic mechanisms, which involve, respectively, covalent catalysis with an aspartate carboxylate as the nucleophile and non-covalent catalysis with a tyrosine that acts as a general acid-base. The emerging new possibilities for enantioselective biocatalytic conversion of epoxides suggests that their importance in green chemistry will grow. 相似文献
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Phosphonous and phosphonic analogues of aspartate and glutamate are substrates of semireaction of enzymatic transamination catalysed by aspartate aminotransferase. 相似文献
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Summary The application of enzymatic interesterification for production of vegetable oils containing omega-3 polyunsaturated fatty acids was investigated. Six veteable oils were used as substrates, together with omega-3 polyunsaturated fatty acid, and reactions were catalysed by immobilized Mucor miehei lipase in organic solvent. The degree of incorporation of eicosapentaenoic acid and docosahexaenoic acid into corn oil, sunflower oil, peanut oil, olive oil and soybean oil were 17.71, 17.59, 16.79, 14.89, 13.91 and 10.48%, respectively, after a 12 h incubation period. 相似文献
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《Biocatalysis and Biotransformation》2013,31(1-4):343-352
Enantioselective bioconversion of organosilicon compounds was successfully carried out with hydrolases and a dehydrogenase. Substituents on silicon atom were found to affect the efficiency of the reactions. In many cases, the characteristics of silicon atom reflected the reactivity. 相似文献
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Sheldon W. May 《Enzyme and microbial technology》1979,1(1):15-22
The oxygenases - enzymes which incorporate molecular oxygen directly into organic molecules - are ubiquitous and of high metabolic significance. These enzymes play crucial roles in the degradation of drugs and foreign substances and in the biosynthesis, interconversion and degradation of amino acids, lipids, porphyrins, vitamins and hormones. Thus, they are centrally involved in the mechanisms of cytotoxicity, mutagenicity, carcinogenicity and tissue necrosis. From the standpoint of enzyme technology, the ability of these enzymes to incorporate molecular oxygen into organic substrates efficiently and selectively is highly enticing, since such reactions are poorly accomplished using conventional chemistry. This review focuses on enzymatic epoxidation reactions, one example of the many chemical transformations catalysed by oxygenases. By way of introduction, an overview of the role of enzymatic epoxidation reactions in the metabolism of polycyclic aromatic hydrocarbons, in steroid biosynthesis and interconversion, and in various other pathways is presented. Following this, enzymatic epoxidation of simple olefins is considered in detail, with emphasis on bacterial systems and discussion of both enzymology and reactivity characteristics. Finally, a number of major issues which must be confronted if complex oxygenase systems are to be utilized in enzyme technology application are briefly discussed. Among these are specialized immobilization techniques, cofactor recycling, problems of enzyme stability, and the intriguing possibility of utilizing mechanistic information in the design of non-enzymatic, chemical model systems which mimic oxygenase catalysis. 相似文献
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Biodiesel can be produced by transesterification of vegetable or waste oil catalysed by lipases. Biodiesel is an alternative energy source to conventional fuel. It combines environmental friendliness with biodegradability, low toxicity and renewability. Biodiesel transesterification reactions can be broadly classified into two categories: chemical and enzymatic. The production of biodiesel using the enzymatic route eliminates the reactions catalysed under acid or alkali conditions by yielding product of very high purity. The modification of lipases can improve their stability, activity and tolerance to alcohol. The cost of lipases and the relatively slower reaction rate remain the major obstacles for enzymatic production of biodiesel. However, this problem can be solved by immobilizing the enzyme on a suitable matrix or support, which increases the chances of re-usability. The main factors affecting biodiesel production are composition of fatty acids, catalyst, solvents, molar ratio of alcohol and oil, temperature, water content, type of alcohol and reactor configuration. Optimization of these parameters is necessary to reduce the cost of biodiesel production. 相似文献
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Min-Hua Zong Toshiaku Fukui Takuo Kawamoto Atsuo Tanaka 《Applied microbiology and biotechnology》1991,36(1):40-43
Summary Bioconversion of three organosilicon compounds of different chain length between the silicon atom and the hydroxyl group (Me3Si(CH2)nOH, n = 1–3) by horse liver alcohol dehydrogenase (HLADH, EC 1.1.1.1.) was studied. Furthermore, the effect of the silicon atom on the HLADH-catalysed reaction was examined in comparison with the corresponding carbon compounds. HLADH could catalyse the dehydrogenation of trimethylsilyeethanol (n = 2) and trimethylsilylpropanol (n = 3). Trimethylsilylethanol was a better substrate than both its carbon analogue, 3,3-dimethylbutanol, and ethanol. The improved activity of HLADH on trimethylsilylethanol could be accounted for by a higher affinity toward HLADH and a lower activation energy of the reaction by HLADH than those of the carbon counterpart. These are derived from physical properties of the silicon atom, that is, the lower electronegativity and the bigger radius than those of the carbon atom. In contrast, HLADH showed no activity on trimethylsilylmethanol (n = 1), whereas it catalysed the dehydrogenation of the carbon analogue, 2,2-dimethylpropanol, fairly well. The reason for the inactivity of HLADH in the case of trimethylsilylmethanol based on the electric effect of the silicon atom is also discussed.
Offsprint requests to: A. Tanaka 相似文献
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Boyat C Rolland-Fulcrand V Roumestant M-L Viallefont PH Martinez J 《Preparative biochemistry & biotechnology》2000,30(4):281-294
The synthesis of new non ionic surfactants is reported. They were prepared from unprotected carbohydrates, amino acids, and fatty alcohols. These modules were linked by enzymatic esterification and transesterification reactions catalysed by lipases and proteases in organic media. 相似文献
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M García-Moreno M Moreno-Conesa J N Rodríguez-López F García-Cánovas R Varón 《Biological chemistry》1999,380(6):689-694
The catalytic cycle of horseradish peroxidase (HRP; donor:hydrogen peroxide oxidoreductase; EC 1.11.1.7) is initiated by a rapid oxidation of it by hydrogen peroxide to give an enzyme intermediate, compound I, which reverts to the resting state via two successive single electron transfer reactions from reducing substrate molecules, the first yielding a second enzyme intermediate, compound II. To investigate the mechanism of action of horseradish peroxidase on catechol substrates we have studied the oxidation of both 4-tert-butylcatechol and dopamine catalysed by this enzyme. The different polarity of the side chains of both o-diphenol substrates could help in the understanding of the nature of the rate-limiting step in the oxidation of these substrates by the enzyme. The procedure used is based on the experimental data to the corresponding steady-state equations and permitted evaluation of the more significant individual rate constants involved in the corresponding reaction mechanism. The values obtained for the rate constants for each of the two substrates allow us to conclude that the reaction of horseradish peroxidase compound II with o-diphenols can be visualised as a two-step mechanism in which the first step corresponds to the formation of an enzyme-substrate complex, and the second to the electron transfer from the substrate to the iron atom. The size and hydrophobicity of the substrates control their access to the hydrophobic binding site of horseradish peroxidase, but electron density in the hydroxyl group of C-4 is the most important feature for the electron transfer step. 相似文献